Fixing git branch detection in Jenkins

Branch detection did not work in Jenkins. I realized that it set
GIT_BRANCH env variable to point to the current branch, so let's try
using this for branch detection.

build_tools/regression_build_test.sh

@@ -26,11 +26,11 @@ function cleanup {
 }
 
 trap cleanup EXIT
-git_branch=$(git rev-parse --abbrev-ref HEAD)
-if [ $git_branch == "master" ]; then
-  git_branch=""
+git_br=$(basename $GIT_BRANCH)
+if [ $git_br == "master" ]; then
+  git_br=""
 else
-  git_branch="."$git_branch
+  git_br="."$git_br
 fi
 
 make clean
@@ -156,7 +156,7 @@ function send_to_ods {
     echo >&2 "ERROR: Key $key doesn't have a value."
     return
   fi
-  curl -s "https://www.intern.facebook.com/intern/agent/ods_set.php?entity=rocksdb_build$git_branch&key=$key&value=$value" \
+  curl -s "https://www.intern.facebook.com/intern/agent/ods_set.php?entity=rocksdb_build$git_br&key=$key&value=$value" \
     --connect-timeout 60
 }